Many sensors used to detect optical radiation are extremely sensitive. Some are capable of detecting less than one microwatt of power. These detectors perform very well when they are used to detect weak sources in a low background scene. However, in a high background scene, such as bright sunlight, the detector responds to the background light making detection of a relatively weak laser pulse impossible. Commercially available detectors do not have a way to prevent the preamplifier from saturating during periods of high input radiation, resulting in degrading performance or shutting off.
Another limitation of prior art sensors systems is a changing noise level. Currently available detectors/preamplifiers have the characteristic of changing noise level as background changes, resulting in reduced sensitivity of the system. No systems currently available use signal sensing or signature analysis to provide discrimination of unwanted signals.
The above problems in existing sensor systems indicate that they cannot be used in areas of high background. The problems listed above are overcome by the present invention.